1. Field of the Invention
The present invention relates to a film forming method used to form an insulating film having a low dielectric constant, a semiconductor device, and a manufacturing method of the same.
2. Description of Prior Art
With regard to a semiconductor integrated circuit device, requests have been made in recent years to achieve not only a higher integration and a higher density but also a higher data transfer speed. Thus, efforts have been actively made to develop an insulating film having a low dielectric constant with a small RC delay (referred to as a low dielectric-constant insulating film, hereinafter).
For the formation of such a low dielectric-constant insulating film, a plasma enhanced chemical vapor deposition method (hereinafter, referred to as PE-CVD method) is known, which uses, as a source gas, a deposition gas consisting of methylsilane (Si(CH3)4, SiH(CH3)3, CH3SiH3 or the like) and nitrogen monoxide (N2O), or a deposition gas consisting of hexamethyldisiloxane (HMDSO) and nitrogen monoxide (N2O).
However, there is an inherent problem in such a conventional method. That is, it is difficult to form a low dielectric-constant insulating film in a stable manner by use of the above deposition gases, the film having, for example, a relative dielectric constant of about 2.7.
Namely, an attempt to reduce the relative dielectric constant creates a problem of a rough surface of the low dielectric-constant insulating film. In addition, an attempt to form a film having a thickness of 2 xcexcm or more creates a problem of cracks in a formed film.
It is an object of the present invention to provide a film forming method, which enables an insulating film to be formed with a low relative dielectric constant about 2.7 or lower while preventing the surface roughness of the insulating film or the generation of cracks in the thick insulating film. Moreover, it is also the object of the present invention to provide a semiconductor device, and a manufacturing method of the same.
The inventors of the present invention made an experiment on two kinds of insulating films formed by PE-CVD, i.e., one formed by use of deposition gas obtained by adding Ar, He or N2 to a major deposition gas component consisting of siloxane and N2O, and then diluting the same, and the other formed by use of a deposition gas consisting of only siloxane and N2O. According to the experiment, as can be understood from FIGS. 3A and 3B or FIGS. 4A and 4B, compared with the latter insulating film, the former insulating film had a great reduction in the surface roughness thereof, and great suppression of the generation of cracks therein.
For use as an alkyl compound containing a siloxane bonding, one can be selected from hexamethyldisiloxane (HMDSO: (CH3)3Sixe2x80x94Oxe2x80x94Si (CH3)3), octamethylcyclotetrasiloxane (OMCTS), and tetramethylcyclotetrasiloxane (TMCTS), the second being represented by a chemical formula 3 below, and the third by a chemical formula 4 below. 